bdr.bdr_conflict_history contains an entry for each conflict generated in the system while Conflict logging is enabled. Unless conflict logging to table is enabled this table will always be empty.
This history table is not replicated between nodes, so each node has separate conflict history records. This is a technical limitation that may be lifted in a future release, but it also saves on unnecessary replication overhead.
It is safe to TRUNCATE this table to save disk space.